I completely agree with your conclusion here. 15 days is
completely
inadequate in many instances, but not all. None the less this
provision
should and I believe must be approved by the ICANN AL membership
before is could be enacted as a requirement.

Although this provision is arguably unfair, it should
be pointed out that ICANN has a more onerous provision
that it imposes on its accredited registrars:

7. a. ...

An SLD holder's willful provision of inaccurate or unreliable information,
its willful failure promptly to update information provided to Registrar,
or its failure to respond for over fifteen calendar days to inquiries by
Registrar concerning the accuracy of contact details associated with the
SLD holder's registration shall constitute a material breach of the SLD
holder-registrar contract and be a basis for cancellation of the SLD registration.

So ICANN's registrar's can cut registrants in 15 days
rather than NSI's 30.

The WIPO Recommendations appear to go even further and make
the SLD revokable at will for furnishing inaccurate contact
information.